As contract negotiations with National Grid go down to the wire, six local utilities unions are poised to strike at midnight on Saturday night, displeased about what they said is a proposal that would hike their health care contribution.

“All locals have taken a strike authorization vote,’ said Brotherhood of Utility Workers Council President Dan Hurley, who said he represents 1,200 workers in six unions in Massachusetts and Rhode Island that constitute “the majority” of National Grid’s electrical workers and the workers in a Northborough call center.

"National Grid is currently engaged in contract negotiations with several union locals. We are negotiating in good faith and are committed to an outcome that balances the needs of our customers and our employees. The safety and well being of our customers, the communities we serve and our employees are our first priorities and will continue to be so as negotiations continue,” National Grid said in a statement.

The company serves about 1.2 million customers in Massachusetts and 842,000 in Rhode Island.

Aside from a proposed health insurance contribution increase from 20 percent to 25 percent, the union members are displeased at the staffing levels, which Hurley said were not high enough to adequately respond to storm damage.

“We’ve seen the consequences in New England and around the country when companies ignore items that impact public safety,” Hurley said in a statement, which also claimed the company has 30 percent fewer workers on staff than in 1996. Hurley told the News Service that the fact National Grid has brought in out-of-state workers to handle cleanup and repairs after major storms is evidence that the company doesn’t have enough trained workers.

Hurley, who is president of Local 369 as well, led his local workers at Pilgrim Nuclear Power Plant through contentious contract talks with Entergy Corp. that resulted in a lock-out after the union authorized a strike. Asked about the chances of a strike versus a last-minute contract extension or an agreement, Hurley said, “We’re committed to negotiating for as long or as hard as it takes to get a deal together.”

The brotherhood, which represents 1,200 workers, also complained about payroll inaccuracies that it said had resulted in a $270,000 fine from Attorney General Martha Coakley.

Last December, the Department of Public Utilities fined National Grid $24.8 million for “systematic failures” in its response to two storms in 2011, which “left local public safety officials standing by downed wires for as long as several days” and other problems.

National Grid serves the outer Boston suburbs, the South Coast, the North Shore, the Worcester area and parts of western Massachusetts.